The present invention relates to an optical module in which a semiconductor light-emitting device and a lens structure are held by a housing while being optically aligned with each other. More particularly, the invention relates to an optical module using a lens structure in which two cylindrical lens portions are respectively located at the positions of first surface (light incident surface) and a second surface (light emission surface), while being oriented orthogonal to each other. The optical module well accepts a semiconductor light-emitting device whose aspect ratio of emitting light is large when it is assembled into the optical module.
An optical module is a part or assembly which holds a semiconductor light-emitting device (e.g., a laser diode) and lenses in a state that the device and lenses are optically aligned with each other, and it is used in a variety of fields. An optical module used in a computer system having a data communication function, for example, includes a semiconductor light-emitting device, lenses, and a housing which holds the device and lenses and fittingly receives a mating ferrule of an optical plug. The semiconductor light-emitting device, and an optical fiber in the ferrule are optically coupled with each other by means of the lenses when the optical plug is coupled to the optical module. An optical module used for a certain type of the bar code reader includes a semiconductor light-emitting device, lenses and a housing for holding the device and lenses in a state that the device and lenses are optically aligned with each other. Light emitted from the semiconductor light-emitting device of the optical module is propagated in space as a beam of a predetermined beam waist.
A spherical lens is usually used for the lens to be assembled into the optical module because such a lens is manufactured easily, highly accurately and inexpensively by only the machining. A radiation pattern of the laser diode of relatively small output power has a profile being substantially circular. Therefore, even when the spherical lens is used, there is less chance that serious problem arises.
In the case of the laser diode of large output power, the light emitted from the diode largely differs, in radiation angle (divergence) and width of the light emitting area, between the horizontal direction and the vertical direction with respect to the active layer (the aspect ratio is large). For this reason, a general spherical lens or a composite lens system including two lens or more can not concurrently adjust the aspect ratio and radiation angle of the emitted light.
To efficiently couple the emitted or radiated light of a large aspect ratio to an optical fiber having a circular cross section, or to propagate the emitted light as a beam having a circular beam waist in space, it is necessary to design the lens having different radii of curvature for the light components of the horizontal and vertical directions. Such a lens is generally an elliptical lens. The curved-surface profile of the elliptical lens is complex. Accordingly, it is technically difficult to manufacture a mold for injection molding.
Accordingly, an object of the present invention is to provide an optical module having a structure which is able to easily and inexpensively realize high coupling efficiency in its coupling to an optical fiber even if a semiconductor light-emitting device of the module is large in aspect ratio and hence its coupling to the optical fiber is difficult.
Another object of the invention is to provide a structure which is able to easily and inexpensively realize an optical module which enables light emitted from a light emitting point to propagate in the form of a beam with a circular beam waist in space even if a semiconductor light-emitting device of the module is large in aspect ratio.
Still another object of the invention is to provide a lens structure which can vary a radiation pattern, as desired, independently between the horizontal direction and the vertical direction, and more particularly to provide a lens structure adaptable for the optical module.
According to an aspect of the invention, there is provided an optical module having a semiconductor light-emitting device and a lens structure, which are held by a housing while being optically aligned with each other. The lens structure includes a pair of cylindrical lens portions, which are oriented orthogonal to each other and located at positions spaced from each other in an optical axis direction.
According to another aspect, there is provided an optical module having a semiconductor light-emitting device and a lens structure which are held by a housing adapted to fittingly receive a ferrule, so that the semiconductor light-emitting device and an optical fiber of the ferrule are optically coupled with each other by the lens structure. The optical module may be constructed as a pig-tail type module in which the ferrule holding the optical fiber is soldered and fixed to the housing. The optical module may be constructed as a receptacle type module in which the ferrule of an optical plug is detachably mounted to the housing. The lens structure includes a pair of cylindrical lens portions, which are oriented orthogonal to each other and located at positions spaced from each other in the optical axis direction.
In each of those lens structure, it is preferable that the cylindrical lens portions are located on both side surfaces of a plate-like base, while being oriented orthogonal to each other, and the lens structure is formed with a one-piece molding piece of transparent resin. The cylindrical lens portion is preferably profiled as a non-spherical surface defined by, for example, the following equation
Z=((1/R)X2)/(1+(1xe2x88x92(1+K(1/R)2X2)xc2xd),
where Z is an amount of cutting measured from a planar surface, and R and K are constants.
In a case where the cylindrical lens portions are located on both side surfaces of a plate-like base, while being oriented orthogonal to each other, and the base and the lens portions are formed as a one-piece molding piece of transparent resin, the effective lens surfaces for the horizontal and vertical optical components of the emitted light can be located at respective positions distanced from a light emitting points using a thickness of the base portion. Further, the curvatures of the lens surfaces can be selected independently in design. Accordingly, optimum design of high freedom is realized.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 11-295876 (filed on Oct. 18, 1999), which is expressly incorporated herein by reference in its entirety.